Insulated conductor.



4 H Patented Mar. ll,l902.. E, THUMSUN Gu -l. G. CALLAN.

INSULATED CONDUCTOR (Application fllsd Nov. 7, 1901.)

(llo Model-9.

h M IWm 'l nvenCom Elihu Thomson and (A) i Chesses b JohnCalf/a]Ian. tmay.

THE nonms PETERS co, PHOTOLITHQ, WASHINGTON, a, c.

UNITED firarns ELIHU THOMSON, OF SVVAMPSCOTT, AND JOHN G. CALL'AN, OFLYNN,

Parent? QE.

MASSACHUSETTS, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A

CORPORATION OF NEW YORK.

ENSULATED CONDUCTOR.

SEECIFICATION forming part of Letters Patent No. 695,127, dated March 11, 1902.

Serial No. 81,442. (No model.)

.To all whom it 12mg concern.-

Be it known that we, ELIHU THOMSON, residing at Swampscott, and JOHN G.CALLAN, residing at Lynn, county of Essex, State of Massachusetts,citizens of the United States, have invented certain new and usefulImprovements in Insulated Conductors, (Case No. 2,060,) of which thefollowing is a specification. I

The object of this invention is to provide an insulating-covering for anelectric con ductor which will have high insulation, will be proofagainst heat and moisture, and will have a minimum thickness withrelation to the size of the conductor.

Conductors are commonly insulated by a winding or braiding of cotton,silk, or other fibrous insulating material or by a solid insulatingcompound, or both. Fibrous coverings, although heat-resisting to aconsiderable degree, are not moisture proof, while the compoundcoverings usually employed not only greatly increase the thickness ofthe conductor, but do not hold up under even moderate heat. XVe producea wire coated with a thin skin of a material flexible, tough, not easilyinflammable; and capable of resisting a comparatively high degree ofheat, these properties rendering it suitable for magnetcoils and otherelectrical purposes where the temperature may range as high as 100 to150 centigrade. WVe carry out our invention by coating the Wire with anumber of adherent films of a relatively non-iniiammable cellulosecompound. Compounds ofcellulosehave heretofore been used-sucl1, forexample, as collodion. This, however, produces an insulationunsatisfactory in several respects. It is extremely combustible andunder appropriate conditions explosive. It will not long endure atemperature much in excess of 75 centigrade, and even at temperatureslower than this it is liable to undergo slow changes which greatlyimpair its insulating properties and may give rise to nitric compoundscapable of acting on the wire, the latter being of particular importancein the case of very fine insulated wire only a few millimeters inthickness. It has also been proposed'to use pure structureless cellulosemade by rovorsi on fromv one of its compounds applied to naked wire. IWe have discovered that other compounds of cellulose-such, for example,as the acetates or the esters, simple or mixed, derived from the othermonobasic fatty acids or the aromatically substituted fatty acids-may besuccessfully applied as a wire-covering. Some of these,in particularthat acetyl compound generally regarded as the tetracetate, arewaterproof compounds of extremely high insulating power and well adaptedfor electrical insulating purposes. tVhen employed alone, however, wehave found them inelastic and somewhat brittle and lacking in adhesionto the Wire; but when they are mixed with a softener-such as certainessential oils, phenol, cresol, or other material having equivalenteffect-they are rendered supple and are not liable to pull apart andleave bare spots if the conductor is stretched in winding or otherwise.We render the coverings uniform by applying a plurality of coatings inthe form of thin films, the cellulose compound being dissolved in asolvent, preferably one very volatile, and the wire being carriedthrough successive baths in Which theseveral films are deposited on thewire. We prefer to effect increased adhesion to the wire by employing apreliminary coating of some adhesive-such as Canada balsam, Veniceturpentine, or rubber. By this means a wire of extremely small.cross-section, as one a few millimeters in thickness, may be effectivelyinsulated, the coating being in thickness only a small fraction of thediameter of the wire and being stable in composition and in insulatingproperties under all ordinary conditions of exposure to the heat andmoisture.

The coating may be done in any suitable apparatus, the bare wire beingled from a reel preferably first through a very thin solution of Canadabalsam, rubber, or other adhesive, which serves the dual purpose ofdissolving any grease from the wire and covering it with a thin adherentcoat, which closely binds to the wire the subsequent coats of cellulosecompound. The wire is led from the adhesive coating bath when usedthrough a dryin g box, which may contain hot air. It is then led throughanother bath and a primary coating of the cellulose compound applied-as,for instance, a solution of cellu lose tetracetate in chloroform 01'other suitable solvent. We have found it advantageous to mix with thissecond application a quantity of Venice turpentine about equal in amountto the actual contents of cellulose acetate in the solution. This givesa coating which adheres closely to the balsam, rubber, or other adhesivefilm used and binds firmly to the wire the subsequent coatings ofinsulating cellulose compound. Second, third, fourth, or furtherinsulating coats of the acetate in solution without the previous largeadmixture of Venice turpentine are applied 'by subsequent baths,flexibility being imparted to the coating by any of the known softenersadded to the solutionsuch as castor-oil, phenol, cresol, the essentialoils, or other materials suitable for the purposepreference being givento those which will withstand high temperatures and that do not easilyvolatilize. They must not undergo decomposition in the presence of themetal of the wire. We have achieved good results by adding to thesolution a softener composed of five parts, by weight, of castor oil andfifty of phenol for each hundred parts of solid cellulose acetatecontained.

In the accompanying drawing is diagrammatically illustrated an apparatusfor coating wire in accordance with our improvements.

1 represents a Wire-reel, from which the wire is led across a groovedwheel 2, dipping in the coating-bath. A number of these Wheels areplaced side by side, dipping in troughs containing solutions of theseveral coating compounds. The wire passes tangentially across a groovein the top of the wheel, the bottom of the wheel dipping in the coatingmaterial contained in a tank 3, divided into the desired number ofchambers by transverse partitions. A scraper 4 may be employed to removethe excess of material from the coating-groove which picks up thecompound from the bath. A scraper 5 may also be employed in the bath toremove any dirt carried around on the wheel. After leaving eachcoating-wheel the wire passes through a hot-air box 6, which may beheated by gas-jets leading from the pipe 7. After applying the firstcoat of balsam, rubber, or other adhesive the wire is led through thedrying-box and over guide-sheaves 8, 9, and 10, back to thecoating-wheel, where the cellulose compound is applied, after which itpasses again through the drying-box and over guidesheaves to the thirdcoating-wheel, and so on in order until all the coats have been applied,after which it is led through a testing-bath 11, of mercury or otherfluid-conductor of sufficient depth around the Wire and Wound on ashipping-reel 12. The mercury-bath is electrically connected with oneterminal of a voltmeter 13, the other terminal of which connects with acircuit of the desired voltage. The wire on the reel 1 is electricallyconnected by a conductor 14 with the other side of the testing source.Thus in case there is any defective spot in the insulation the voltmetergives a Visible indication and the defect may be cured before the wireis reeled. A suitable audible signal may replace or supplement thevoltmeter.

We have attained the best results with the cellulose ester known astetracetate of cellulose. vention specifically to this material. Othercellulose esters not readily inflammable might also be employed as, forexample, the esters of the other monobasic fatty acids, formic,propionic, butyrie, due, the esters of the aromatically substitutedfatty acids, such as benzoic, phenyl-acetic, or phenyl-propionic, or theesters of oleic, angelic, and several other acids not included in theclasses mentioned. The structureless insoluble modification of celluloserecovered through the decomposition of viscose or cellulose xanthatemight also be used. A similar covering might be made for insulatingpurposes on other forms of material than wires as, for example, a filmmay be deposited on condenser-plates and serve as the dielectric of thecondenser.

What we claim as new, and desire to secure We do not, however, confineour in-.

by Letters Patent of the United States, is

1. An insulating compound consisting of an inherent non-explosivecellulose ester attached to a support.

2. An insulating compound consisting of a non-explosive cellulose esterattached to a support by an adhesive binder.

3. An insulated conductor coated with a non-explosive cellulose ester.

4. An insulated conductor coated with a cellulose ester bound to theconductor by an adhesive compound.

5. An insulated conductor coated with a waterproof heat-resistingcompound of structureless cellulose.

6. An insulated conductor coated with an acetic of cellulose.

7. An insulated conductor coated with tetracetate of cellulose.

8. An insulated conductor coated with a ELIHU THOMSON. JOHN G. CALLAN.

Witnesses:

DUGALD McK. MOKILLOP, JOHN J. WALKER.

